1. Field of the Invention
The present invention relates to diaphragm valves. In particular, the present invention relates to diaphragm valves which allow for free-drainage of a valve body of the valve when the valve is in the open position.
2. Description of Background Art
The demand for higher quality products forces industries to continually re-evaluate fundamental and basic elements of their processes in a search to discover new methods and better components that will yield greater uniformity with higher levels of reproducibility in order to achieve the quality desired. Evaluation of inspection results by United States Food and Drug Administration (FDA) inspectors in recent years has caused that agency to push industry to focus on cleaning validation and, of particular relevance to this disclosure, the cleanability of equipment, a large part of which is sanitary valving. Among the concerns are that some equipment in these processes may not be adequately cleanable in place, that in-situ cleaning procedures are not themselves adequate to clean the equipment installed or that the procedures and equipment are appropriately matched, but the procedures are not being properly executed.
Valves are by far the largest category of equipment used in processes. Relative to other existing valve designs, weir-style diaphragm valves are simple, provide good process isolation, cost-effective to install and maintain and because they were thought to be easily and reliably cleanable in place. Unlike several other categories of valve designs, weir diaphragm valves generally offer good drainability with little hold-up of material when properly installed. For these reasons they have, over the last fifty years, become the valve of choice for use in hygienic processes.
In recent years the performance of these valves has been subject to much greater and closer scrutiny, at least in part due to pressure from FDA. While still the preferred choice for some applications, it has become apparent that weir diaphragm valves can pose a significant risk as a source of cross over contamination, particularly if improperly installed, operated and maintained or if clean-in-place and sterilize-in-place procedures are not properly followed. These concerns stem from the basic design of weir diaphragm valves. Referring to FIG. 10 of the present invention, a typical weir diaphragm valve 101 is illustrated. The weir diaphragm valve 101 includes a valve body 103, a diaphragm 133 and a bonnet, as well as other typical valve components (all not shown).
In FIG. 10, a static perimeter or circumferential seal 136 is formed between the valve body 103 and the bonnet by a perimeter of the diaphragm 133. Furthermore, a dynamic line seal 137 is formed along a weir 140. The main problem with the weir diaphragm valve design is that the static circumferential seal 136 is continuous with the line seal 137 made by the diaphragm 133 across the top of the weir 140. When the center portion of the diaphragm 133 is raised to break the line seal 137 across the weir 144 to allow for flow through the valve, pressure is applied to the inner edge of the diaphragm 133 where it forms the static circumferential seal 136 with the valve body 103. Accordingly, a portion of the static circumferential seal 136 is also raised. When the line seal 137 is reformed across the weir 140 by lowering the diaphragm 133, material is trapped between the inner edge of the diaphragm 133 and the valve body 103, i.e., within the static circumferential seal 136. This trapped material may migrate back into the internal cavity 113 of the valve body 103 over time. Although this may be less of a problem while a batch of a process is in progress, not completely removing the trapped residual during cleaning procedures between batches is a more serious issue and may be considered very critical between campaigns of different products by the FDA.
In addition to the above, weir valves in the past were typically used in an orientation where the flow through the valve proceeded from the inlet passage to the outlet passage by flowing vertically over the weir 140. Accordingly, material would be trapped on the upstream side of the internal cavity 113. This of course causes cross contamination.
Manufacturers today, in an effort to improve drainage through their valves and minimize hold-up, recommend that weir diaphragm valves be cantilevered over onto the side so that fluids can flow passively around the weir and out, rather than vertically over the weir. While this is necessary in order to make weir valves drain, this also places a portion of the circumferential seal 136 at the bottom of the valve, causing it to become a sump where material will tend to collect and where complete drainage will be very difficult to fully achieve. Consequently, a more significant cleaning challenge and possible point source for cross contamination is exacerbated when using a weir valve in this manner. Several articles can be found through the literature on the subject of weir-style valve cleanability. One of the most recent is an article in Pharmaceutical Processing (September, 2001, pg. 80) in which the author, in a comparison study of weir valves and radial diaphragm valves, demonstrates that weir valves frequently do not become fully cleaned. In this study, radial diaphragm valves provided much higher clean-in-place reliability.
Accordingly, the primary alternative valve design to weir valves that has gained favor in many industries is the radial diaphragm valve, similar to the testing in the study mentioned above. FIG. 11 of the present invention illustrates a typical radial diaphragm valve 101. As with weir diaphragm valves, radial diaphragm valves include a flexing diaphragm 233 that allows the valve 201 to be opened and closed while segregating the mechanical elements of the valve 201 from the process. Radial diaphragm valves, however, differ from weir diaphragm valves in several important ways. The most important advantage radial diaphragm designs offer is that the static circumferential seal 236 between the valve body 203 in a radial diaphragm valve is not continuous with the dynamic seal 237, as is the case with weir valves. Since the two seals are not continuous, a radial diaphragm valve can be actuated without the circumferential seal 236 being affected. Accordingly, cross contamination as a result of residual hold-up in the circumferential seal 236 is effectively eliminated when compared to the weir diaphragm valve.
While it would seem that the solution to the cross contamination problems currently plaguing the industry could be resolved by radial diaphragm valves, it is a byproduct of the radial design that makes radial diaphragm valves a less perfect solution to the problem. As mentioned above, radial diaphragm valves are defined by the segregation of the circumferential seal 236 from the flow control or dynamic seal 237 and the passage it seals. A review of the background art will show that in the dynamic seal 237, the flow control passage 224 and the mating annular dynamic sealing surface 237 immediately about it are positioned at the center of the internal valve cavity. Accordingly, the flexible portion 241 of the diaphragm 233 between the static circumferential seal 236 and the dynamic seal 237 is enough to allow the necessary range of movement of the dynamic sealing tip 235 of the diaphragm 233 to seal the flow control passage 244, while minimizing stress on the flexible portion 241 of the diaphragm 233. In view of this, the portion of the diaphragm 233 which mates with the valve body 203 at the circumferential seal 236 is not lifted. Accordingly, material is not trapped in the circumferential seal as in a weir valve.
As can be readily understood, with the arrangement of radial diaphragm valve, an opening into the internal cavity 213 of one flow passage 226 is located radially outward from the centrally placed flow control passage 224 and radially inward from the circumferential seal 236. It will also be noted that the surface of both of these passages open into the valve internal cavity 213 through the same wall 242. The wall 242 is substantially planar or dished as illustrated in FIG. 11, and at least one of the axes of the flow passages tends to enter the internal cavity 213 at close to a right angle.
As a consequence of the combination of the orientation of the passages relative to the wall 242 of the internal cavity 213 through which they enter, the opening of one fluid passage 224 is positioned centrally in the internal cavity 213 with the other passage 226 positioned radially. Furthermore, both passages are within the circumferential seal 236. Accordingly to the background art, radial diaphragm valves can only be made to fully drain if they are oriented vertically, i.e., with the outlet at the bottom, and will only drain if the bottom of the outlet is adjacent the circumferential seal 236. Accordingly, in FIG. 11, it would be necessary to orient the valve 201 such that the passage 226 is oriented downward.
As can be readily understood, since radial diaphragm valves are only completely drainable if oriented in a vertical manner, there are severe limitation on how radial diaphragm valves found in the background are can effectively be used. Specifically, orienting a radial diaphragm valve in a vertical orientation results in a significant vertical drop across them. Due to the numerous valves required for some systems, orienting all of the valves in a vertical manner is not possible because of the space limitations. Accordingly, radial diaphragm valves have not displaced weir diaphragm valves in practice, in spite of the in-situ cleanability limitations of weir diaphragm valve designs.